..::www.jezwells.org::..

Computer music tools

My research and teaching at the University of York are primarily concerned
with audio recording, processing and modelling. Teaching materials and
research output often take the form of software tools for audio
processing and computer music. Some of these are available from this
page. Since they were not developed for commercial exploitation some
are probably not quite as efficient, gainly or bug-free as they might be (particularly the older ones - some more than ten years old!) . However I have recently (2012) begun a series of 'science in the
studio' plugins which are intended as educational aids as well as audio
processing tools and these are subject to more rigorous testing. That said, all of
these tools are provided with no guarantee and anyone
downloading and using them acknowledges that I accept no responsibility
at all for any problems arising from their use. There are some VST
plugins (PC only at the moment I'm afraid), impulse responses for
use
with sampling reverbs and Matlab
functions. If you do use them, let me
know how you get on (jez[at]jezwells[dot]org) and report any bugs or
problems so I can look into how they might be resolved in future
versions.

If
you are interested in hearing the differences in quality between HE-AAC
coding (AAC+, part of MPEG 4) and mp3 (MPEG 1 layer 3) at low bit rates
there are some audio examples you can download as a zip file (4 MB) here.

Science in the Studio VST plugins

These plugins are intended to illustrate and demonstrate the science of
common studio processing tasks. They can be freely downloaded and used
either as studio tools, just like other VST plugins, or they can be
used to investigate and learn about a particular aspect of sound
engineering.

The first of these (May 2012) is a combined amplitude and time based
panning tool called FranPan (named after Franssen who investigated
panning in the middle of last century as an employee with Philips). The
plugin (for 32 bit Windows) can be downloaded here.
The documentation, which includes guidance on installation and use, as
well as background information and suggestions for
educational/experimental activities can be downloaded here.

The
latest addition (June 2012) is FlexDelay, a flexible delay plugin which
can be used to explore extreme Doppler shifting as well as direct
implementation of common
'thickening' effects such as chorus and flanging. The
plugin (for 32 bit Windows) can be downloaded here.
The documentation, which includes the usual guidance on installation and use, as
well as background information on how the processor works along with suggestions for
educational/experimental activities can be downloaded here.

Other VST plugins

There are three different plugins here. Two of them are implementations
of algorithms originally developed by Christopher Penrose (thanks for
his blessing and assistance in doing this) and the other is an
extension of some research done by John Szymanski and Phillipe Mergen
at the University. All three plugins make use of the Intel Signal
Processing Library which provides highly optimised signal processing
routines such as Fourier and wavelet transforms. They run best on Intel
processors but they also work fine on the AMD Athlons on which they
have been tested. Before you can use any of the plugins you need to
install the files contained in this zip file
in to the windowssystem32 folder of your computer

Ether

A spectral compositing algorithm developed by Christopher Penrose, this
implementation goes a little further in allowing simple magnitude and
phase swapping between sounds. There is a user guide
and the plugin dll
which goes in the vst plugins folder of whichever application you want
to use it with.

Shapee

This is a fantastic cross-synthesis algorithm devised by Christopher
Penrose which uses a technique he refers to as 'frequency shaping'.
Using this plugin you take a choral
recording and combine it with an orchestral recording
to produce this combined
version. As for Ether there is a user
guide and a dll
file
which needs to go in your vst plugins folder. It currently only works
in mono (2 in, 1 out) but inspired by the multichannel capabilities of
programs such as Reaper I will be doing a stereo (4 in, 2 out) version
soon. There is a stereo implementation available as a Matlab function,
below.

Wavethresh

There are a couple of plugins here that I produced when I was first
looking into wavelet processing for audio. They are spectral
thresholding processors (you can see a DAFx paper I wrote about this in
the publications section of this site). There are two versions and both
are available here since the functionality of both are slightly
different. There is a
user guide and dll
for version 1 and some release notes and a replacement dll for version 2
(don't have both versions in your vst plugins folder at the same time -
otherwise your host applications might get confused).

One application of wavelet thresholding is to realistically change the
perspective on stochastic type sounds. This example
demonstrates how a rain storm can be thinned to a shower by slowly
decreasing just one parameter, the deterministic threshold, over
time.

I produced a study using solely this version 1 of this plug-in on two
stereo tracks of audio. Fourier thresholding is used (sometimes very
subtly) on the harmonic material, wavelet thresholding (sometimes very
unsubtly) is used on the drum loop. This was produced in Logic Audio
Platinum 5.5 and uses the automation system in this program to get the
most out in WaveThresh by varying the parameters in real time. You can
download it here: requiem internal.
This piece received its premiere at Sheffield University Sound
Junction's Works for
Peace concert.

The sinusoidal extraction added in version 2 allows WaveThresh
to adapt to the incoming signal and use the most appropriate processing
method for different parts of the signal. In the following audio
examples a piano recording is divided into sinusoidal (deterministic)
and non-sinusoidal (stochastic) components and these are then
individually thresholded and re-added to remove the background hiss.

Impulse responses

As part of restoration work on some choral recordings made
in
the late 1950s in the cathedrals of Arundel and Ely, I went to visit
these two buildings last Summer to make recordings of the acoustic
'signatures' (otherwise known as impulse responses) of these buildings.
Impulse response can be used in sampling reverberators (such as the
free SIR
VST
plugin). There are three impulse responses: one taken in the nave of
Arundel, one taken in the choir of Ely and one taken in the Lady Chapel
at Ely. They are in 44.1 kHz, 24 bit .wav format:

Many thanks to Damian Murphy for his advice and loan of equipment for
making these recordings. Damian has made many impulse response
recordings of weird and wonderful spaces and these are available from Space-Net of
which he is a co-founder. The Hamilton Mausoleum recording is
incredible! There's also a description of the technique used to make
these recordings.

Matlab functions

There will be more functions to follow
but for now
there are just two, a stereo implementation of Christopher
Penrose's Shapee algorithm and a function to generate signals for capturing impulse responses based on the work of Angelo Farina. These
were written and tested in Matlab 7 but it should work in versions
5 and 6 too. Let me know if you would like these adapted for use in Scilab.

Shapee

Instructions for using the
function can be accessed by typing 'help
shapee' at the
Matlab command prompt (once you have copied the m file into your 'work'
or other Matlab directory). It is the same algorithm as is used in the
VST plugin version above, but it works on stereo files and in double,
rather than single, precision floating point.

Logarithmic sweep generator

This function generates a logarithmic frequency sweep with user-specified
start and stop frequency, sample rate and duration. The inverse sweep
is also generated - filtering the sweep with its inverse produces an
impulse. Sweeps are often used for impulse response measurement since
they contain much more energy than an actual impulse (and so offer an
impulse response recording with a much better signal to noise ratio).
Inverse filtering the 'sweep response' of a building, processor etc.
gives the impulse response of that system. This function is based on
Angelo Farina's paper Simultaneous measurement of impulse response and distortion with a swept sine technique.